1) Field of the Invention
The present invention relates to a technology for calculating mutual immittance in an electric circuit apparatus and mutual immittance used to calculate an electromagnetic-field strength, based on a moment method.
2) Description of the Related Art
Conventionally, a radio wave that is unnecessarily emitted from an electric circuit apparatus interferes with other radio waves such as TV and radio, and hence it is strictly restricted in each country. In order to satisfy such restriction of radio waves, it is necessary to use various technologies as solutions to this problem such as shield engineering and filter technology. Further, a technology that quantitatively simulates how much these technologies can reduce the radio wave is required.
Huge amount of processing time is necessary for a computer to simulate such an electromagnetic wave analysis, and hence an apparatus that computes the strength of an electromagnetic field emitted from the electric circuit apparatus at a high speed is required.
The strength of an electromagnetic field emitted from an arbitrarily shaped object can be easily calculated by using a known theoretical formula if the current flowing through each section of the object is known. Theoretically, if the Maxwell's electromagnetic wave equation is solved under a given boundary condition, a current value can be obtained. However, at present, solutions to the equation to be directly obtained under a complicated boundary condition targeting an arbitrarily shaped object has not been known yet.
Therefore, all the solutions for determining the current, used in the electromagnetic-field strength calculation apparatus are approximate, though the degree of difficulty is different. The moment method is currently known as a representative of the approximate solutions.
The moment method is one of the solutions to an integral equation derived from the Maxwell's electromagnetic wave equation, and this method can handle a three-dimensional arbitrarily shaped object. More specifically, the object is divided into small elements to calculate a current.
As described above, since the moment method can handle a three-dimensional arbitrarily shaped object, a configuration in which the strength of an electromagnetic field emitted from the electric circuit apparatus is calculated by using the moment method is prevailing in the electromagnetic-field strength calculation apparatus.
When the moment method is used, such a method is employed that when a metal object is handled, the metal portion is formed into a mesh, as a target for analysis, to obtain a mutual immittance Zi,j between the divided metals, and simultaneous equations [Zi,j] [I1]=[Vi] in the moment method established between the mutual immittance Zi,j, a wave source Vi and a current Ii flowing in the divided metal is solved to obtain a current Ii, and the electromagnetic-field strength to be emitted is calculated from this result. A symbol [ ] denotes a matrix.
One of references relating to the moment method is as follows.
[Reference 1] H. N. Wang, J. H. Richmond and M. C. Gilreath: “Sinusoidal reaction formulation for radiation and scattering from conducting surface”, IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, vol. AP-23, 1975.
When an electromagnetic wave is analyzed with respect to an actual machine (electric circuit apparatus), generally, an analogous model is repeatedly analyzed, while changing a part of the analysis model.
In the conventional electromagnetic-field strength calculation apparatus, as described above, even if the analysis model is slightly changed, mutual immittance is calculated for combinations of all elements, which requires huge calculation amounts. The calculation of the mutual immittance accounts for nearly half the time required for the electromagnetic analysis.
Therefore, when the electromagnetic wave analysis is performed with respect to the actual machine, the calculation amount becomes huge by the number of times of changing the part of the analysis model, causing a problem in that even several hours to tens of hours are required.